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4-PORT RS-232 PCI AND HS PCI SERIAL ADAPTERS
Appendix B. Electrical Interface
Quite possibly the most widely used communication standard is RS-232. This
implementation has been defined and revised several times and is often referred to
as EIA/TIA-232. The IBM AT
®
computer defined the RS-232 port on a 9-pin D sub
connector and subsequently the EIA/TIA approved this implementation as the
EIA/TIA-574 standard. This standard is defined as the 9-Position Non-Synchronous
Interface between Data Terminal Equipment and Data Circuit-Terminating
Equipment Employing Serial Binary Data Interchange. Both implementations are
in widespread use and are referred to as RS-232 in this document. RS-232 is
capable of operating at data rates up to 20 kbps at distances less than 50 ft.
(15.2 m). The absolute maximum data rate may vary due to line conditions and
cable lengths. RS-232 is a single-ended or unbalanced interface, meaning that a
single electrical signal is compared to a common signal (ground) to determine
binary logic states. The RS-232 and the EIA/TIA-574 specification define two types
of interface circuits, Data Terminal Equipment (DTE) and Data Circuit-
Terminating Equipment (DCE). The adapter is a DTE device.
